3GPP Release 13 introduces discussion of partial coverage scenes, and introduces a concept of Device-to-Device (D2D, which is a direct communication technology between devices introduce in 3GPP Release 12, and is realized by introducing an auxiliary link and is not realized by uplink and downlink of a cellular network system) relay, that is, two or more than two terminals for performing D2D communication, in which, some terminals are located in a coverage area of a network and some terminals are located out of the coverage area of the network. Specifically, as shown in FIG. 1, a partial coverage scene diagram is shown. In the schematic diagram, a relay user equipment (UE) can establish a Radio Resource Control (RRC) connection between a base station, the base station can configure D2D transmission resources for the relay UE, and a remote UE communicates with the relay UE using pre-configured resources. The remote UE can also be located in the coverage area of the network, in such situations, the base station can directly configure D2D communication resources for the remote UE.
At present, RAN2#92 does not explicitly define an RRC state of a remote UE in coverage. The remote UE can be in an idle state, and can also be in a connected state. If the remote UE in the coverage needs to enter the idle state, a base station side does not need to maintain the context of the remote UE. It is represented that if the remote UE in the coverage selects a relay UE, the remote UE needs to initiate signaling to the base station for releasing the UE context; otherwise, the UE cannot enter the idle state. However, if the remote UE is changed into the idle state in this manner, limitations on D2D resource usage is brought. In this way, a UE in the idle state cannot use D2D transmission resources in a scheduling mode, only resources in a resource pool mode can be used. Thus, such a UE state transition limits the flexibility of resource when the remote UE is performing the D2D communication. Particularly, when resource pool is configured insufficiently and scheduling resources are more, the utilization of the D2D communication resources is descended.
Therefore, it is a problem that how to solve a state transition and connection management of a remote terminal in the coverage, needs to be solved, so as to avoid low utilization of the D2D communication resources.